1 Copyright © 2009 by ASME 

Proceedings of the ASME 2009 Rail Transportation Division Fall Conference 

RTDF2009 

October 20-21, 2009, Ft. Worth, Texas, USA 

RTDF2009-18016 

DETAILED IMPACT ANALYSES FOR DEVELOPMENT OF THE 

NEXT GENERATION RAIL TANK CAR 

Part 1 – Model Development and Assessment of Existing Tank Car Designs 

Steven W. Kirkpatrick 

Applied Research Associates, Inc. 

Mountain View, CA, USA

ABSTRACT 

Significant research has been conducted over the past few 

years to develop improved railroad tank cars that maintain tank 

integrity for more severe accident conditions than current 

equipment. The approach taken in performing this research is 

to define critical collision conditions, evaluate the behavior of 

current design equipment in these scenarios, and develop 

alternative strategies for increasing the puncture resistance. 

The evaluations are being performed with finite element 

models of the tank cars incorporating a high level of detail. 

Both laboratory scale and full-scale impact tests were 

performed to validate the modeling and ultimately compare the 

effectiveness of current and alternative equipment designs. 

This paper describes the development of the detailed finite 

element model of the tank car and the use of the model for 

impact and puncture analyses. The validation of the model 

using the results of the full-scale impact tests is presented. The 

subsequent application of the model to assess the puncture 

resistance of existing tank car designs is discussed. 

INTRODUCTION 

Accident statistics show that the rail industry’s safety 

performance has generally improved over the last few decades. 

The Federal Railroad Administrations (FRA) Railroad Accident 

and Incident Reporting System (RAIRS) show that the number 

of accidents per year with at least one car releasing hazardous 

materials has decreased significantly over the past 25 years, as 

shown in Figure 1 [1]. However, a series of three recent 

accidents or derailments involving the release of hazardous 

material have focused attention on the structural integrity of 

railroad tank cars. These events include (1) Minot, ND, on 

January 18, 2002; (2) Macdona, TX, on June 28, 2004; and (3) 

Graniteville, SC, on January 6, 2005 [2-4]. 

Figure 1. Number of Accidents with at Least One Car 

Releasing Hazardous Materials [1]. 

To better define the collision threat, studies have been 

performed to both evaluate the accident statistics [e.g. 5-7] and 

analyze the kinematics of freight trains in derailments and 

collisions [e.g. 8, 9]. Evaluation of the derailments and 

collisions has shown that these are complex events with a wide 

range of collisions between the various cars in the train. A 40 

mph derailment of a large freight train may involve thirty or 

more cars and the derailment event would last on the order of a 

minute before the train comes completely to rest. 

An example of a derailment simulation for a 36-car train 

model is shown in Figure 2. Impacts on tank cars will include 

both head impacts and side impacts from objects as small as a 

broken rail to very blunt objects, such as another tank head. 

Thus, the objective of the tank car development efforts 
 2 Copyright © 2009 by ASME 

included increased protection in both head and side impacts for 

a range of impact conditions. 

(a) 36-car train derailment model 

(b) Calculated response 25 seconds after derailment 

Figure 2. Calculated derailment behavior for the 36-car train 

model [9]. 

To develop an improved tank car design, the physics of the 

tank impact response need to be understood. For the purposes 

of the analyses performed here, the impactor is assumed to be a 

rigid object. As the impactor strikes the tank, the tank starts to 

deform. As it deforms, it will develop resisting forces. For a 

given tank configuration (e.g. tank thickness, internal pressure 

level) and a given impact condition (e.g. head or side impact, 

centered or offset impact location) the tank will have a 

characteristic force-deflection curve, such as that shown in 

Figure 3. The shape of this force-deflection curve is relatively 

independent of the size of the impactor. The area under the 

force-deflection curve is equal to the amount of impact energy 

that has been dissipated. If the impact speed is sufficiently low, 

the total energy will be dissipated and the impactor will be 

safely stopped. If the impact speed is too high, the forces 

developed will exceed the strength of the tank material and the 

tank will be punctured. The point at which this failure of the 

tank is initiated will depend strongly on the size of the 

impactor. 

To absorb additional energy prior to puncture, you can 

increase the force levels required to deform the tank, increase 

the displacements that can be experienced prior to puncture 

initiation, or a combination of both larger forces and larger 

displacements. The protection strategies are to add external 

energy absorbing structures and protective layers. These 

structures may have a larger standoff distance to extend the 

total displacement and energy dissipation prior tank rupture. 

Other protection strategies may be to (1) reinforce the tank 

system (increasing forces), or (2) blunt the impact loads 

(increasing the allowable tank displacements prior to rupture). 

Figure 3. Characteristic force-deflection curve for a tank 

impact. 

A research program was initiated to develop strategies for 

improving railroad tank cars so they can maintain tank integrity 

for more severe accident conditions than current equipment. 

The Next Generation Rail Tank Car (NGRTC) research 

program was initiated by The Dow Chemical Company (Dow), 

Union Pacific Railroad, and Union Tank Car Company, 

working under Memoranda of Cooperation (MOC) with the 

Federal Railroad Administration, and Transport Canada, and 

separately with the U.S. Transportation Security 

Administration. 

The NGRTC Project was organized to include a Core Team 

(consisting of representatives from the signatories to the MOC) 

and a group of Lead Contractors. The Core Team and Lead 

Contractors worked together to: 1) evaluate and select 

candidate materials, components, subsystems and systems with 

the potential to provide large performance improvements in the 

safety and security of rail tank cars; 2) select conceptual tank 

car designs incorporating appropriate materials, components 

and systems for improved safety and security; and 3) develop 

and use appropriate models, analytical techniques and testing 

protocols to demonstrate the efficacy of the tank car concepts. 

The goal of the NGRTC program was to develop a conceptual 

tank car that had a five to ten times improvement in the impact 

energy required to puncture the tank car. 

A key effort in this program is the development and 

application of detailed finite element models of tank cars which 

can accurately predict the puncture resistance under different 

impact conditions [10]. These analysis tools were developed 

and validated for the puncture of the baseline tank cars for both 

side and head impact conditions. The models were 

subsequently applied to assess the puncture resistance of 

various tank car designs. 
 3 Copyright © 2009 by ASME 

This paper describes results from the NGRTC project to 

develop strategies for improving railroad tank cars so they can 

maintain tank integrity for more severe accident conditions 

than current equipment. The scope of this effort includes the 

development of detailed finite element models for tank cars and 

the use of those models for various impact scenarios to assess 

puncture energies. A summary of the testing performed under 

the NGRTC program is also provided in this paper, since it was 

critical for the development and validation of the puncture 

modeling capability. The primary emphasis of this paper is on 

the development and validation of the finite element analyses 

and the application to current tank car designs. In a companion 

paper [10], the analysis methods are applied to assess the 

potential of advanced tank car protection concepts. 

BASELINE TANK CAR IMPACT MODEL 

The first task in this research was to develop and validate a 

modeling capability that can be used to analyze the impact 

response of a tank car. The model developed for the 105J500 

chlorine tank car is shown in Figure 4. The model includes all 

of the primary tank car structures including the jacket and 

jacket standoffs, commodity tank, manway, bolsters, stub sills, 

and the addition of the outriggers attached to the draft gear to 

prevent a post-test rollover of the target tank caused by the 

rebound off the reaction wall in the impact testing. 

Figure 4. Updated model of a 105J500W pressure tank car.

Another feature of the tank impact model was the addition 

of an explicit model of the lading. The lading model consists 

of a low strength viscoelastic material that fills the same 

volume as the slurry lading in the test tank cars. The sloshing 

of the lading model can be seen in the cutaway view of the 

predicted impact response shown in Figure 5. This lading 

modeling approach was established to capture the momentum 

transfer of the coupled fluid-structure response but minimize 

effects such as sloshing at the fluid free surface that can cause 

numerical stability problems. 

Full-scale impact tests were performed on tank cars and 

tank heads [11-13] and the results were used to validate the 

models. The tests were fully instrumented with accelerometers, 

string potentiometers, pressure gauges, and strain gauges. 

These measurements were compared to the model predictions 

to validate the model. Overall, very good agreement was 

obtained between the prediction and test for the various 

measurements made. An example of the agreement is the 

comparison of the predicted and measured force-deflection 

curves, shown in Figure 6. This force-deflection curve is an 

important characteristic of the tank car for a given impact 

scenario. The area under the force-deflection curve is the 

impact energy that is dissipated (the primary measure used to 

assess the puncture protection levels). The comparison of the 

force-deflection behaviors shows good agreement between the 

calculation and the test. 

Figure 5. Calculated Test 1 impact response with cutaway 

showing lading.

Figure 6. Comparison of the measured and predicted Test 1 

force-deflection curves.

MATERIAL DAMAGE AND FAILURE BEHAVIORS 

The other necessary component of a predictive tank car 

puncture modeling capability is a detailed model that can be 

used to determine the impact damage and failure of the tank 

and protective system materials. An extensive program of 

laboratory materials testing was performed to characterize the 

tank car materials of interest. The tests included various 

material characterization tests, such as notched tensile tests [14] 

and combined tension/shear tests [16]. These tests were used to 

develop the parameters for the material constitutive and failure 

models. Strain rate effects on the tank car materials were 

investigated and found to not have a significant effect on the 

tank puncture behavior. Additional component tests, such as 
 4 Copyright © 2009 by ASME 

punch tests and bend tests, were performed to validate the 

constitutive models. 

The material damage and failure model applied is the BaoWierzbicki (BW) model [17-19] that defines the material 

damage development based on the current stress state in the 

material and the plastic strain increments. This model is an 

extension of previous ductile damage models [e.g. 20-24] that 

included the effects of stress state on ductility for primarily 

tensile stress states. The critical strain function is that proposed 

in the BW criterion and contains multiple branches depending 

on the range of stress state, as shown in Figure 7. The critical 

strain in each branch are governed by the equation 

( )

( )

( ) ( )

[ ] ( ) ( )

( ) ( ) ⎪

⎪

⎪

⎪

⎩

⎪

⎪

⎪

⎪

⎨

⎧

≤

− + ≤ ≤

− ≤ ≤ +

∞ ≤ −

=

mean eq

mean eq

mean eq mean eq

mean eq

mean eq

mean eq

c mean eq

B

B A A

A

σ σ σ σ

σ σ σ σ

σ σ σ σ

σ σ

ε σ σ

3

1

3

3

1 9( ) 0

0

3

1

1 3

3

1

2

where the parameters A and B can be determined by a series of 

tests under different stress conditions including notched tensile 

tests, with specimens of varying notch radii [25], and tensileshear tests with different ratios of tension to shear stress. 

Figure 7. Bao-Wierzbicki failure surface and tests used for 

model calibration. 

Although these material tests were used to develop the 

constitutive and failure model parameters, the resulting 

constitutive models were used to simulate the tests. This 

provides a validation that the material parameters were 

properly incorporated into the analyses and that the constitutive 

and failure model is capable of simulating the range of material 

behaviors under different loading conditions. The first of these 

material test series was the notched round bar (NRB) tests [14, 

26]. The primary material of interest described here is the 

TC128B tank car steel. A comparison of the calculated and 

measured stress-strain behavior across the notch for the three 

different radii specimens is shown in Figure 8. The comparison 

shows that the constitutive and damage model were capable of 

reproducing both the increase in stress level and reduction in 

ductility that occur as the notch radius is reduced. The BW 

failure parameters used provide a good correlation to the 

observed failures of the specimens. 

Figure 8. Validation of the notched round bar test behavior for 

TC128B. 

A similar comparison of the calculated and measured loaddisplacement behaviors for the combined tension/shear tests 

[16] are shown in Figure 9. The comparison shows again that 

the constitutive and damage model were capable of 

reproducing both the decrease in load level and increase in 

displacement that occur as the orientation was rotated from 

pure tension to pure shear. The BW failure parameters used 

provide a good correlation to the observed failures of the 

specimens. 

Figure 9. Validation of the combined tensile shear test behavior 

for TC128B. 

For the various steels evaluated in this program, the 

component punch test was the primary laboratory material test 

used to validate the constitutive and failure models [27-29]. An 

example of a model and simulation of a punch test on a 0.488-

inch-thick TC128B plate is shown in Figure 10 [28]. The 

corresponding comparison of measured and calculated punch 

force-displacement curves for a series of three different tests on 

the TC128B plate is provided in Figure 11. In addition to the 
 5 Copyright © 2009 by ASME 

force-deflection curve, the final profile of the plate specimens 

after the punch tests were digitized and compared to the 

analyses. Again, the overall agreement between the testing and 

analyses was good. This agreement provides a further 

validation that the BW failure model is appropriate for 

predicting puncture of the tank cars. 

Figure 10. Simulation of the punch test on the thin TC128B 

plate material. 

Figure 11. Force-deflection curves for three punch test 

configurations on TC128B. 

TANK CAR PUNCTURE MODELING 

The BW failure modeling capability was combined with 

the tank car model to complete the tank car puncture prediction 

capability. The approach used was to develop a user-defined 

constitutive model that was incorporated in the LS-DYNA 

finite element code [30]. The tank model was also simplified in 

these puncture analyses to have quarter-symmetry by removing 

the manway, bolsters and lading. The simulation of the full 

scale tank car impact test (Test 2 - above the puncture 

threshold) was performed using the tank puncture model, as 

shown in Figure 12. The model shown was reflected vertically 

about the symmetry plane (seen as a line in the figure) for 

improved visualization of the impact behavior. The impactor in 

this analysis was a rigid 6x6 inch ram with a 0.50-inch radius 

around the edges and a total weight of 286,000 lbs. The small 

rectangular patch of elements under the impactor (already 

punctured in Figure 12) is the fracture zone where the BW 

failure model was applied. The remainder of the tank structure 

was modeled with 4-node shell elements and a tied shell-tosolid constraint was used at the interface of the two regions. 

Figure 12. Simplified tank model analysis with BaoWierzbicki failure assessment. 

The comparison of the measured and calculated forcedeflection behavior for Test 2 with the tank puncture model is 

provided in Figure 13. The comparison shows overall good 

agreement between the calculation and test. The peak load at 

which the tank was punctured was very accurately captured by 

the model. The measured puncture force was 940,000 lbs and 

the calculated puncture force was 915,000 lbs. The primary 

discrepancy of the test and model was a slightly more 

compliant behavior in the model seen at the large 

displacements. This difference in compliance could primarily 

be attributed to the removal of the manway from the tank 

model in this analysis. As a result of the larger displacements 

in the analysis, the calculated puncture energy of 1.26 million 

ft-lbs is higher than the measured puncture energy of 0.87 

million ft-lbs. 

Figure 13. Tank puncture model Test 2 analysis with BaoWierzbicki failure assessment. 
 6 Copyright © 2009 by ASME 

This combined tank car impact and puncture modeling 

capability was applied to evaluate a wide range of tank/jacket 

and head/head shield geometries. The side impact condition 

was a normal impact centered on the belt line of the tank. The 

head impact condition was an offset impact point 

approximately 29 inches vertically downward from the center 

of the head. 

An example head impact and puncture analysis is shown in 

Figure 14. The head impact analyses included the head, head 

shield, and a sufficient length of the side shell and jacket to 

allow for buckling to initiate in the jacket support from the 

loads transmitted by the head shield, as seen in Figure 14. 

 (a) Initial conditions (b) Puncture response 

Figure 14. Calculated puncture behavior of a head and head 

shield. 

The calculated puncture force for each of the different 

head and shell impact analyses are plotted against the combined 

head and jacket (or head shield) thickness in Figure 15. All of 

the analyses included in the figure are performed with the 6x6 

inch impactor. The figure shows the analyses are mostly 

consistent with a linear relationship between puncture force and 

total thickness of the protective layers. 

The linear relationship between the puncture force and 

total tank system thickness provides an indication of the 

primary failure mechanism initiating the tank puncture. The 

geometry of the ram impacting and indenting a pressurized tank 

shell is shown in Figure 16(a). A force balance analysis in the 

direction of the impact on a patch of tank shell material is 

shown in Figure 16(b). The forces resisting the impact loads 

are the pressure on the inside surface of the contact patch and 

the shear stress around the perimeter of the contact patch. For 

a 100 psi tank pressure and a 6x6 inch impactor, the pressure 

load is less than 4 kips on the contact patch. Thus, the average 

shear stress is approximately equal to the impact force divided 

by the product of the impactor face perimeter and tank 

thickness. 

The slope of the linear fit in Figure 15 corresponds to an 

average shear stress in the tank layers around the perimeter of 

the impactor of 39 ksi. By comparison, the yield and ultimate 

stress levels of the TC128B in pure shear are 33 ksi and 49 ksi, 

respectively (approximately 58% of the stress values in pure 

tension using a Von Mises yield criterion). Thus, the failure 

mode is primarily exceeding the shear capacity around the 

perimeter of the impact patch. 

Figure 15. Calculated puncture forces as a function of system 

thickness. 

(a) Geometry of the tank indentation 

(b) Free body diagram for the tank contact patch 

Figure 16. Loading and failure mechanism for the tank impact 

and puncture. 
 7 Copyright © 2009 by ASME 

The calculated puncture forces for pressurized heads and 

the thicker head systems tended to fall slightly below the linear 

fit in Figure 15. The proposed mechanism for these lower 

forces is that, for the stiffer head systems, the offset impact 

creates a larger stress concentration along the upper edge of the 

impactor face and the failure initiates at that location at a lower 

total force. The more compliant head systems allow for a 

larger dent to form and the impactor develops a more uniform 

stress distribution in the impact patch around the ram face 

perimeter. 

The calculated puncture energies for all of the side and 

head impact analyses are plotted against the combined 

thickness of the system in Figure 17 (6x6 inch impactor only). 

When comparing all of the puncture energies the data falls into 

four separate groups that are distinguished by the impact type 

(side or head) and the tank pressure. Again, the comparison 

indicates that the total thickness is the relative parameter that 

determines puncture energy for a given impact condition and 

pressure level, indicating that a retrofit design with an 

increased jacket thickness should provide equivalent protection 

to a thicker commodity tank systems with equivalent combined 

shell and jacket thicknesses. 

Figure 17. Calculated puncture energies as a function of 

system thickness. 

The above correlation of the system thickness and puncture 

energy can be converted to assess system requirements for a 

given impact scenario. The relationship between the impact 

speed and impact energy for the 295,000 lb ram car is provided 

in Figure 18. This impact energy is proportional to the mass of 

the object so a 286,000 ram car would have energies that are 

three percent lower than those in Figure 18. This relationship 

between speed and impact energy can be combined with the 

linear fits between system thickness and puncture energy 

(shown in Figure 17) to determine the required system 

thickness to resist puncture for a specified impact speed. 

Examples of the pressurized (100 psi) Cl tank car thickness 

requirements to resist a puncture of the 6x6 inch impactor at 

various impact speeds is shown in Figure 19 for both side and 

head impacts. The figure shows that as the impact speed 

increases, the system thickness required begins to increase 

rapidly. A 25 mph side impact would require approximately 

three inches of steel to prevent puncture and a 30 mph head 

impact would require more than six inches of steel. Obviously, 

these protection levels are not achievable with a traditional tank 

car design approach while maintaining a tank car that is 

economically viable as a result of both the initial tank car cost 

and the drastically reduced lading capacity. 

Figure 18. Relationship between impact speed and kinetic 

energy for the ram car. 

Figure 19. Puncture prevention thickness requirements for 

various impact speeds. 

The analyses demonstrate that the 25 and 30 mph impact 

protection levels are not feasible for the 6x6 inch impactor. 

However, the additional analyses demonstrate that they would 

be achievable with a larger ram size. The puncture energies 

from analyses of side impacts on 500 lb and 600 lb tanks using 

6-inch, 9-inch, and 12-inch square impactors are shown in 

Figure 20. The figure shows that the 25 mph ram car impact (6 
 8 Copyright © 2009 by ASME 

million ft-lb impact energy from Figure 18) is approximately 

equivalent to the puncture energy of the 600 lb tank car 

impacted by the 12x12 inch ram. 

Figure 20. Summary of puncture energies for chlorine tank 

cars for various impactor sizes. 

SUMMARY AND CONCLUSIONS 

This paper describes the development and validation of 

detailed analysis methodologies for predicting the impact 

response and puncture potential of railroad tank cars. The 

primary impact threat considered was a 6x6 inch impactor. For 

the systems analyzed here, this impactor acts like a relatively 

small punch and the primary failure mode is a punch shear 

failure around the perimeter of the impactor face. 

Analyses of traditional tank car designs show that the 

puncture force for the 6x6 inch impactor is roughly 

proportional to the combined thickness of the tank and jacket 

(or head and head shield). Thus, a reasonable amount of 

additional puncture protection can be achieved by increasing 

the thickness of the tank or increasing the thickness of the 

jacket and head shield. 

The impact energy dissipated prior to puncture depends on 

the compliance of the tank under he specific impact conditions. 

A more compliant tank or impact orientation allows for a larger 

indentation length before the tank exceeds the puncture force 

threshold and, as a result, dissipates a larger amount of impact 

energy. The side impact orientation was more compliant than 

head impacts and increasing the pressure in the tank reduces 

the compliance of the system. 

ACKNOWLEDGMENTS 

The contents of this paper are based primarily on work 

funded by The Dow Chemical Company, on behalf of the Next 

Generation Rail Tank Car (NGRTC) Project. The development 

of the puncture modeling methodologies and the testing used to 

validate the models and develop the constitutive and failure 

models were all performed under the NGRTC project. The 

analyses of the Ethylene Oxide (EO) tank cars were funded by 

the American Chemistry Council, Inc., on behalf of its Ethylene 

Oxide Panel. 

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